WebSearch: new Add-to-Search Interface

* New search box interface that contains both simple search and advanced
  search (javascript dependent).  (addresses #622)

* Replaces the 3-line advanced search, with only 1-line add-to-search,
  with the possibility of adding patterns to the current search pattern.

* Ammends regression tests to take into account a third search
  interface.

* Moves the config variables `CFG_WEBSEARCH_ENABLED_SEARCH_INTERFACES`
  and `CFG_WEBSEARCH_DEFAULT_SEARCH_INTERFACES` from the `inveniocfg.py`
  to `search_engine_config.py` and `invenio.config`
  respectively.  (closes #271)  (PR #1738)

Signed-off-by: Ludmila Marian <ludmila.marian@gmail.com>
Co-authored-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
WebSearch & WebAlert: Your Searches improvements

* Moves page "Your Searches" from WebAlert to WebSearch and
  under the /yoursearches/ URL. Updates all the respective URLs
  and function calls. Moves function account_list_searches()
  from WebAlert to WebSearch.

* Separates the popular alerts page from the user searches page
  and creates new separate function for popular alerts the user
  can choose from to set up new alerts.

* Fixes various doc strings, variable and function names.

  (closes #880)
WebSearch: yoursearches interface improvements

* Redesigns the "Your Searches" page.

* Adds the "Search into your searches" functionality.

* Fixes a few small bugs.

  (closes #881)
WebAlert: youralerts interface improvements

* Redesigns the "Your Alerts" display interface.

* Adds new functionality to display alerts based on
  a specific search query.

  (closes #882)
WebSearch: fix yoursearches string format bug

* Fixes a small bug that caused special characters that
  had been replaced by the urllib.quote() function to crash
  during the string formatting.

  (closes #883)
WebSearch & WebAlert: CSS fallback to default

* Changes some CSS attributes to match yoursearches and
  youralerts style to the default Invenio style.

* Changes the order of the Personalize menu to be in alphabetical
  order again after the addition of Your Searches.

* Deletes some previously added unneeded images.

  (addresses #884)
WebSearch: more CSS fallback to default

* Changes the arrows used for page navigation in the
  Your Searches page to match Invenio's default arrows.

* Deletes the respective previously added images files.

  (closes #884)
WebAlert: paging for youralerts

* Introduces page navigation support for the
  "Your Alerts" page.

  (closes #885)
WebAlert: Searching for youralerts

* Introduces searching in the user's defined alerts based on
  the alerts' names and arguments.

* Fixes small bug in the paging navigation that caused a crash
  when no alerts were to be displayed.

* Adds user confirm step before permanently deleting an alert.

  (closes #886)
WebSearch: Fix paging bug in yoursearches

* Fixes small bug in the paging navigation that caused a crash
  when no searches were to be displayed.

* Introduces fix that skips querying the database again when there
  are no matching user searches.

  (closes #887)
WebAlert & WebSearch: fix kwalitee reported issues

* Fixes various warnings and errors reported by kwalitee.
WebStyle: add new images to the Makefile

* Adds new images for yoursearches and youralerts to the Makefile
WebAlert: option to pause and resume alerts

* Adds the option to pause and resume alerts. The option can be
  configured either in when editing a specific alert or when
  displaying all the alerts.

(closes #1227)
Webalert & Websearch: prettify display list header

* Prettifies the display list header for Your Alerts and Your Searches
  by adding the paging navigation information.
Webalert: smart display of popular alerts link

* Hides the link to the popular alerts if there are none already defined.
Webalert: improve store results in basket menu

* Improves the appearence of the "Store results in basket?" menu.

* Links the basket name to the basket display when displaying alerts.
Webalert & Websearch: harmonize display

* Harmonizes and prettifies the display of "Your Searches" and "Your Alerts"
Websession: Revamp the "Your Account" page

* Revamps the "Your Account" page by arranging items to be
  displayed in a 3-column grid, trying to keep all columns
  equal in size.

* Re-arranges code for consistency and readability.
General: fix kwalitee reported issues

* Fixes various warnings and errors reported by kwalitee.
Miscutil: fix get_authenticated_mechanize_browser

* Fixes the string checked in get_authenticated_mechanize_browser to make
  sure that the user was logged in correctly.